The bucket-ends of shovels used in open pit mine operations are typically composed of a large central body to hold and move material with a rear door for dumping. The doors are typically a hinge-style design and, if not controlled, will swing wildly when opened or closed. The door can contact the main boom when opened and can impact the bucket structure when closed. Repeated door impacts will cause the bucket structure to fatigue and crack. Impact noise is an issue.
To reduce door-induced damage and noise, the industry installs various types of door-rotation inhibiting devices in an effort to reduce the momentum of the door. Of these, the majority are variations of either a friction-disk or a hydraulic design.
Friction-disk designs offer excellent resistance torques in relatively small packaging envelopes when adjusted properly; however, torque quickly reduces as friction plates wear. Maintenance and adjustment is frequent to maintain good performance. The required maintenance cycle is impractical and seldom followed leading to poor overall performance.
For various reasons, hydraulic designs do not match the high-torque versus small-size combination offered by friction disks; however, maintenance on hydraulic units is typically not required once they are operational so the overall performance is better than the previous option. However, hydraulic units have design challenges of their own. Among these are torque adjustability, ease of installation, fluid volumetric changes due to temperature, and internal pressure spikes.